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The Origin of Modern Humans: The Fossil Evidence, Part 3

Today's entry was written by
James Kidder.
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Note: In this ongoing series, James Kidder writes about human evolutionary history. Today’s post is part three of a series in which James discusses the evidence for the origins of modern humans by exploring key paleoanthropological discoveries from around the world. Read last week’s post here.

East Asia

The fossil record for early modern humans is considerably more fragmentary in East Asia than in Africa or the Near East. While there is a documented transition in China between the late Homo erectus population at Zhoukoudian to the archaic Homo sapiens remains of Dali and Mapa (described in the last post in this series), there is little in the way of transitional forms from the latter to modern humans. Subsequent to the appearance of these crania, the next hominins that factor into the origins of modern humans in East Asia are the Liujiang and Zhiren Cave fossils.

Zhiren Cave

Also located in the Guangxi Zhuang area, Zhiren Cave yielded several teeth and a large section of a human mandible. Using extinct animal correlations and uranium series dating, the remains are thought to be between 100 and 106 thousand years old (Figure 9). The remains are distinctive in that a clear chin is present on the mandible. This is a trait that is only found on modern humans. If the date holds up (and at this point, there is no reason to suspect otherwise) then it would signal a migration of modern humans out of Africa sometime between 100 and 150 thousand years ago.

Three other East Asian sites with skeletal remains, although dated very late, are worth mentioning: Zhoukoudian Upper Cave, Tianyuan Cave, and the Japanese Minatogawa site. While the Tianyuan Cave has produced only postcranial fossils, the associated date by AMS Radiocarbon is between 35 and 33 thousand years B.P. As Kaifu and Fujita (Kaifu & Fujita, 2012) note, these remains are indistinguishable from modern populations and denote the appearance of clearly modern humans in this area by 40 thousand years B.P. One of the problems unique to the Japanese archipelago is that, due to the acidity of the soil, no human remains of any kind have been found dated prior to this.

Figure 10: Upper Cave 101

The Zhoukoudian Upper Cave remains consist of three complete crania (101-103), and some mandibular and postcranial fragments. Unfortunately, like the Zhoukoudian Homo erectus remains, they were lost during the run-up to World War II and only casts survive. Equally distressing is that skull number 102 was crushed post-mortem and no attempt was made to reconstruct it before it was cast, so no usable measurements can be taken from it. The other two crania show a confusing pattern of relatedness to other regional populations and studies have variously pegged them as Southeast Asian, European, African and Native American in morphology. Further adding to the confusion is that the date for the remains cannot be bracketed any more tightly than 12 to 30 thousand years B.P. Consequently, for all intents and purposes, it looks like they simply dropped out of the sky. Our research indicated that the 101 cranium (Figure 10) fell within the range of the modern human sample but only if size was controlled (Kidder et al., 1992). The cranium is larger than most modern humans but proportionally so.

The Minatogawa remains, from the Island of Okinawa, are more securely dated to around 24 thousand years B.P. (Baba, Narasaki, & Ohyama, 1998) and are thought to have their origin in Southeast Asia. These remains consist of an almost complete skeleton and three partial skeletons that are demonstrably modern in appearance.

It is difficult to draw evolutionary patterns in this region other to state that it appears that modern humans were there by around 100 thousand years ago. When they got there is currently unknown. It is further, nigh impossible to compare the scope and trajectory of the change from archaic Homo sapiens to modern Homo sapiens here. Liujiang has very few archaic traits and the Zhiren Cave remains are simply too fragmentary to draw comprehensive conclusions of any kind.

Pope (Pope, 1992) has argued that some characteristics that are present in the Liujiang cranium, such as a flattened frontal bone, rectangular eye orbits and a flat midface can be found on the Dali specimen, but also admits that, given the modernity of the find, the early date is “remarkable.” Regarding Zhiren Cave, while Liu and colleagues (Liu et al., 2010) have described the mandible as modern, they note that, overall, it is large and robust and may provide a link to populations that came before. At this point, however, given the information we have for this region, we simply do not know.

Australasia

Figure 11: Willandra Lakes Hominid 50

The earliest securely dated remains in Australasia are from the Australian sites of Lake Mungo and Willandra Lakes. Lake Mungo yielded the remains of several individuals, all of which are thought to be around 57-62 thousand years B.P (Thorne et al., 1999). Lake Mungo 3 is an almost complete, flexed burial with morphological characteristics that are very gracile with no archaic characteristics whatever (Bowler & Thorne, 1976).

The Willandra Lakes Hominid 50 specimen (Figure 11) was discovered as a burial in New South Wales in 1980 and is bracketed between 12.2 and 32.8 ky B.P., younger than the Lake Mungo burial (Grün et al., 2011). The mostly complete vault is very long and robust, with a low forehead and a prominent brow ridge. The morphology of this skull has led Hawks et al. (Hawks et al., 2000) and to argue that it has direct links to the Ngandong fossils and represents continuity from archaic Homo sapiens to modern Homo sapiens in this region.

Arguing against this perspective, of course, is that the Lake Mungo cranium is earlier and much more modern. It, therefore, has been suggested that there were independent migrations into this area represented by each of these populations. This is, however, equally problematic since the Lake Mungo locality is within the Willandra Lakes region and the two sites are very close together. Given the recently discovered variability in the synchronic Dmanisi remains, it therefore seems reasonable to argue that the two different specimens represent morphologically variable diachronic populations in the area. Whether they are, then, the direct descendants of the Ngandong population is not known.

Conclusion

The appearance of the modern human form is, based on these data, staggered in timing and is, perhaps, partially topographically dependent. While it seems that modern humanity gets its beginnings in North Africa, there is rapid migration out to both the Near East and the Far East. What is not clear is the relationship between the archaic Homo sapiens populations and the moderns. We know, based on the genetic evidence that will be examined in a future post, that there was mixing with the locals such that Neandertal genes exist to this day in European populations. How much mixing is still unclear, however. Further, as we shall see, there was as yet another genetically distinct population from the Neandertals and early moderns, represented by a single finger bone found in Denisova Cave, in the Steppes of Eurasia, northeast of Kazakhstan. Do these three groups represent a highly polytypic species that interbred at the peripheries of their ranges? Do they represent a syngameon, different species that interbred at the peripheries only when necessary? These questions are still being debated in palaeoanthropological circles.

One thing is clear from this survey, however: the earliest sites with modern human remains have been securely dated to greater than 150,000 years ago. While young earth creationists have attempted to denigrate and dismiss modern radiometric methods, such attempts have been without success. These methods are extremely robust and very well understood.

As importantly, however, no early modern human remains have been discovered in the Fertile Crescent, the area where it is presumed that the activities recorded in the early chapters of Genesis took place. In fact, this region has yielded no concrete human remains prior to the Neolithic period, some 8,000 to 10,000 years ago.

These two points have profound implications for the traditional understanding of the Garden of Eden account. The appearance of modern humans at this early date exceeds any literal reconstruction of the biblical texts in Genesis involving the appearance of Adam and Eve. Further, the placement of these earliest moderns strongly suggests that they cannot be incorporated into any version of the events of Genesis 2-4 as traditionally understood. They seem to be completely extraneous to the story. If this is the case, how are we to interpret these chapters?

Were Adam and Eve, as some have suggested, Neolithic farmers, being only two of many people alive at the time? Is the story of Adam and Eve symbolic, representative only of humans as a whole? While the palaeontological evidence alone is not sufficient to answer these questions conclusively, these data strongly suggest that while either of these options is viable, a straight, literal reading of the text is not.

Next: the archaeological evidence concerning the origin of modern humans.

Brown, P. (1999). The first modern East Asians? Another look at Upper Cave 101, Liujiang and Minatogawa 1. Interdisciplinary Perspectives on the Origins of the Japanese, International Research Center for Japanese Studies, Omoto (ed.) Kyoto, 105-130.

Somebody should point this out to Hugh Ross from reasons.org who tries not to resort to science denialism but also thinks that modern humans only began to disperse from mesopotasmia between 15,000 and 12,000 years ago.

PNG - #85918

July 1st 2014

Jim, in the absence of being able to measure the fertility of ancient populations in matings with each other (biological species criterion,) what does “species” mean to a paleoanthropologist? Do you do some measurements on the fossils and decide how many standard deviations will be regarded as a species difference? I realize now there are ways of estimating the amount of mixing that occurred from sequences of ancient genomes, but if you don’t have that, how do you decide what to call different species?

Jimpithecus - #85921

July 1st 2014

Well, this is the sixty-four thousand dollar question. When Theodosius Dobzhansky formulated (and Ernst Mayr extended) the Biological Species concept, in 1937, it was the first clear formulation of what exactly a species was. George Gaylord Simpson came along and said “Wait a minute. That’s all well and good for animals that are live and for who’s behavior we can account. What about extinct ones?” This led to a concept known as the evolutionary species concept, where you would recognize a species in the fossil record based on its morphology as well as its successors and precursors and sort of eyeball when species “changed.” That was phenetics. Everyone in the 1940s through to the 1960s grew up on this. It was not until the late 1960s that the notion of lineage splitting came about, with the work of Willi Hennig. He ushered in cladistics. Species were then identified in the fossil record not on their chronological position but, rather, on whether or not they had plesiomorphic or “retained” traits or apomorphic or “derived” traits. The study of trait polarities led to what we now know as systematic taxonomy or systematics. In this way of thinking, species are related based on the number of traits they share. This study formed the basis for Punctuated Equilibrium (Punkeek), the brainchild of Stephen Jay Gould and Niles Eldredge. This tends to work very well at the higher taxonomic groups but gets fuzzy when you start talking about species within the same genus. Are we looking at two species with similar traits or interspecific variation within a species? This is a heck of a problem in trying to identify early Homo. At one point, there are two very different forms on the landscape at the same time, one very large and the other quite small. Is this sexual dimorphism or are they separate species? This has led to disagreements about whether or not to accept Homo ergaster and Homo heidelbergensis as separate species or whether to lump them together and call it intraspecific variation. Let me know if you come up with an answer.

Jimpithecus - #85922

July 1st 2014

Sorry, that first “interspecific” should have been “intraspecific.”

PNG - #85923

July 1st 2014

Hey, I do genes. Bones are too wonderful for me.

Jimpithecus - #85928

July 2nd 2014

So now the comment that had been removed is back and my response to it is gone? Curiouser and curiouser.